Albert Barnes Commentary Jeremiah 29:23

"because they have wrought folly in Israel, and have committed adultery with their neighbors` wives, and have spoken words in my name falsely, which I commanded them not; and I am he that knoweth, and am witness, saith Jehovah." — Jeremiah 29:23 (ASV)

Villainy - Elsewhere folly, in the sense of lewdness (Judges 20:6), unchastity.